The present invention relates, in general, to lasers and, more particularly, to Vertical Cavity Surface Emitting Lasers (VCSELs).
Semiconductor lasers such as VCSELs are used to generate an optical signal, e.g., light, in optical communication systems, Compact Disc (CD) players, bar code scanners, etc. Typically, a VCSEL in forward bias will not lase over all the area which is being electrically pumped, either due to high loss edge regions or because of the optical mode profile which is being supported. The intensity of the optical signal generated by the VCSEL is dependent on the amount of current flowing in the active region, i.e., the larger the current, the greater the intensity of the optical signal.
A potential problem with VCSELs is the generation of a secondary or undesirable optical signal (also referred to as an optical tail) upon removal of the electrical input signal. Secondary optical signals result because some areas within the VCSEL have a greater carrier density than other areas within the VCSEL, i.e., the carrier distribution within the VCSEL is non-uniform. More particularly, the carrier density is greater in the areas of the VCSEL that are not lasing than in the areas of the VCSEL that are lasing. When the electrical input signal is removed, carriers from the higher carrier density portions diffuse towards the lower carrier density portions of the VCSEL and can result in these portions being able to lase again, leading to a secondary output signal. This signal can reach levels as high as 20 percent of the maximum amplitude of the primary optical output signal. Secondary optical output signals can reduce system performance and result in the transfer of erroneous data.
Accordingly, it would be advantageous to have a laser device and method for preventing secondary optical output pulses. It would be of further advantage for the laser device and method to be compatible with standard semiconductor processes and be cost efficient.